IDT Low Power Thermal Sensors for DDR2 and DDR3 Memory Modules

Hi, my name's Rami Sethi from IDT. I'll be talking today about IDT's new family of ultra-low power thermal sensors, primarily optimized for memory module applications. 

 

Thermal sensors have become used quite commonly in memory applications, primarily because both volatile and non-volatile memory can have data integrity sensitivity at high temperature. Thermal management is critical in a lot of enterprise and storage applications nowadays. And some key areas where thermal sensors are used are register DIMM, ECCU DIMMs, and small outline DIMMs and DDR3 and DDR2 applications, as well as solid state disks. 

 

There are several usage models and methods that thermal sensors are used to control DRAM temperature. Primarily, they're used to provide a closed loop thermal algorithm for controlling temperature and maintaining data integrity, one example of which is closed-loop thermal throttling, or CLTT. 

 

Typically, the temperature is read over an interface, either I2C or SM-Bus, or it can be read through an event-driven pin. And at high temperatures, that temperature reading is then used to perform one of several actions. One may be throttling the bandwidth between the memory control with the DRAM. To reduce temperature, that’s called closed-loop thermal throttling. Another would be adjusting the DRAM refresh rate to maintain data integrity. And a third may be increasing or decreasing fan speed in the system. Finally, at critical temperatures, there may be a shutdown or data backup function that would be triggered. 

 

Some of the key benefits in the system of CLTT are enhanced reliability, basically enhanced data integrity, improved bandwidth performance and efficiency, because the DRAMs will operate in a very optimal temperature range, lower overall system power, as opposed to open-loop type of configurations, and better acoustics by having better fan control. 

 

There's an optional feature on some of the devices, which is a serial presence detect, or SPD. The SPD is basically 256 bytes of EEPROM, the lower 176 of which are used to configure DIMM information and configuration, information for the system. The upper 80 bytes are used for user-configurable information, and so that can be used for anything such as statistical storage, event logging, or any other function. 

 

There are several modes of operation for the thermal sensor in terms of how the event pin behaves. 

 

The first is interrupt mode. In interrupt mode, basically every time a temperature threshold is crossed, the event pin will assert and needs to be de-asserted, essentially through software. Essentially generating an interrupt to the system. 

 

The second mode is comparator mode. In comparator mode, the even pin will assert every time a temperature threshold is crossed and will automatically clear on the subsequent crossing. 

 

And the finally is T-critical mode. T-crit mode essentially only observes the TCRIT temperature setting which would be the highest level temperature typically used to trigger an emergency event like system shutdown. 

 

Each of the limits has programmable hysteresis to avoid metastability problems with the thermal sensor if you're hovering around a given temperature. 

 

If you look at the block diagrams for each part, they look very similar. The real difference between the TSE2002 and the TSE3000 is the fact that the 2002 has an additional 256 bytes of EEPROM, which is called the serial presence detect. Other than that, all other blocks are common between the two. You have an analog temperature sensor that basically actually senses the local air temperature around the device. You have a sigma-delta converter, which basically converts the analog signal to a digital signal, which is 12 bits resolution. You have your register space, which is actually a register space that's industry standard and defined by JEDEC JC 42 and you have your SM-Bus and I2C interface. 

 

Some of the key features and benefits of the family are industry leading temperature accuracy of plus or minus one degree Celsius over the full -20 to 125 degree range, compliance to the full standard set forth by JEDEC 42.4 for these devices on DIMM modules. SM-Bus and I2C compatibility for maximum system flexibility, 3.3 and 2.5 volt capability for backwards compatibility to previous and forward compatibility to next generation SM-Bus and I2C controllers, ultra low standby current, which saves power in both mobile and battery backed applications such as storage, very fast EPROM write time, less than three milliseconds, which is less than half of the required specification and increases ATE and system efficiency. High resolution, all the way down to 1/16 of a degree Celsius, is available for very fine loop control of thermal throttling algorithms. And input glitch filtering and power on hysteresis is also available to maximize system availability and robustness. 

 

So that covers most of the major features and benefits of the family. I want to thank you for watching and we'll see you next time.